According to an advantageous method of manufacturing cards incorporating various electronic elements, the electronic elements are coated or embedded in a resin that forms a core or intermediate layer of the card. EP Patent No. 0 570 784 generally discloses a manufacturing method of this type. In order to obtain a core that has flat, uniform surfaces, it is preferable to coat all of the electronic elements incorporated in the card and thus to cover the electronic display with the resin coating. In this latter implementation made, the resin must be transparent at least in the display area. The transparency of the resin causes a problem as regards obtaining high quality printing, in particular on the top surface of the card where the display appears. Consequently, it raises a dual problem. Generally speaking, printing patterns on a transparent layer causes a decrease both in colour intensity and contrast, so that the colours have a translucent appearance. Secondly, the presence of various electronic elements in the transparent core causes variations in light reflected by the core, which results in darker areas on the surfaces of the core. The support on which a pattern is printed is thus not optically uniform, which generally leads to variations in contrast and variations in colour intensity on the top surface side of the finished card.
In order to overcome the aforementioned problem, in manufactured cards of the prior art, a light-coloured, preferably white, ink or varnish is deposited underneath the printed patterns relative to the core of the card, via a silkscreen printing technique, so that the thin layer of ink or varnish has a certain thickness. Two variants of cards made in accordance with this technique are shown in FIGS. 1 and 2.
Card 2 of FIG. 1 is formed of a core 4 incorporating an electronic unit 8 and an electronic display 10. These electronic elements 8 and 10 are embedded in a transparent resin 6 that forms core 4, which is made in a first step of a manufacturing method for such cards. Core 4 is formed by a technique known to those skilled in the art, in particular in a press or by injecting the resin into a mould. Next, a transparent film 12 is arranged on the top surface side of the core, on the inner surface of which a pattern 14 is printed. To obtain high quality printing, i.e. high definition, printed patterns 14 are preferably obtained by an offset printing technique. Then, according to this prior art method, a layer of ink or varnish 16 is printed on pattern 14. This layer 16 is preferably white and it extends over the entire bottom surface of transparent film 12 except for the display area located above electronic display 10. Layer 16 thus defines a window through which electronic display 10 is visible.
Likewise, a transparent film 18 is arranged on the bottom surface side of the card 2, on the top surface of which a pattern 20 is printed. This pattern 20 is covered by a layer of ink or varnish 22. Layer 22 is also preferably deposited by silkscreen printing. However, it should be noted that bottom layers 16 and 22 might be deposited by various techniques.
Card 22 according to the variant shown in FIG. 2 includes a core 24 formed of a resin or any material 26. Core 24 differs from core 4 of FIG. 1 in that the electronic display 10 at the top surface thereof is flush with the top surface of core 24. Unlike the preceding variant, material 26 does not have to be transparent here. Material 26 may be added in liquid form in a press or injection moulding installation, as for core 4 of FIG. 1. In another method of manufacturing core 24, electronic display 10 can be inserted in a shell with a preformed housing or in the aperture of a layer forming core 24, which may be formed of one or several layers assembled by lamination or by press bonding. In order to have a flat, uniform support for printing pattern 14, a transparent film 30 is arranged on the top surface of core 24. A layer of ink or varnish 16 is deposited on the top surface of film 30, leaving a window for electronic display 10. Pattern 14 is printed on this bottom layer 16 by an offset technique. A transparent external film 12 is then assembled to printed film 30. A fine layer of adhesive or resin is provided between printed film 30 and external film 12 to increase adherence between these two transparent films. On the bottom surface side of card 22, an opaque layer 32 is arranged against the core, on the bottom surface of which a pattern 20 is printed. This pattern 20 is then covered by a transparent external film 18 by means of a thin layer of adhesive or resin 36.
Besides problems linked to the thickness of card 22, when developing the present invention it was observed that embodiments of cards 2 and 22 did not efficiently resolve the previously identified problem, i.e. the problem of a decrease in contrast and low colour intensity due to the presence of a transparent layer or film behind the printed patterns 14. Two major problems appear with the embodiments described with reference to FIGS. 1 and 2.
First of all, the deposition of layer 16 by a printing technique does not provide a perfectly opaque background. Various experiments have demonstrated that it is necessary to deposit several layers particularly by silkscreen printing in order to obtain an opaque background providing a satisfactory visual appearance for high quality cards. Moreover, the inks or varnish that can produce this opaque background 16 are the type that have two components. Such inks or varnish have a relatively long drying time, which raises several manufacturing problems. Thus, the time necessary for printing or depositing several layers of varnish or ink for the opaque background is considerable. This raises a storage problem during the drying periods for each print or ink or varnish deposition. This results in a relatively expensive manufacturing method requiring a large storage capacity. This storage is not easy either since the printed films must not be touched during the drying periods.
The second major problem is the problem of adherence of the transparent external layer 12 in finished cards 2 and 22. The patterns 14 made by an offset printing technique adhere relatively poorly to the transparent plastic film 12. To increase the adherence of this external layer, printed pattern 14 is generally either covered with a thin layer of adhesive or resin that adheres well to the transparent plastic film used. If the two bottom layers 32 and 18 of card 22 are laminated to each other with a printed pattern 20 and fine layer of adhesive 36 between them, the adherence between layers 32 and 18 is sufficient. It was observed that this is due to the fact that adhesive 34 slightly penetrates the printed pattern and creates a multitude of anchorage points with the layer or film on which pattern 20 is printed. In other words, printed pattern 20 is sufficiently permeable to the adhesive for the latter for form a real adherence interface between the two plastic films or layers. The same effect is observed in the case of a similar card to that of FIG. 1 where only printed patterns 14 and 20 are provided. By selecting a resin 6 that adheres well to transparent layers 12 and 18, these layers have sufficient adherence to core 4 because resin 6 penetrates slightly printed patterns 14 and 20 during the card lamination assembly operation. Thus, it has been observed that the presence of the bottom layer forms a barrier to the adhesive or to the resin such that they can no longer ensure the proper adherence of layer 12 in cards 2 and 22, and respectively of layer 18 in card 2.